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New study says that, unlike humans, Chimpanzees don't experience menopause
MINNEAPOLIS / ST. PAUL ( 12/13/2007 ) -- Researchers have found no evidence that chimpanzees in the wild undergo menopause in the way that women do, according to a new report in the Dec. 19 Current Biology, a Cell Press publication. That's despite the fact that reproduction tends to diminish at a similar age in both species. The study draws on data from chimpanzees at several sites in Africa, including Gombe National Park, where Jane Goodall began her pioneering work in 1960. The Gombe data is now stored at the University of Minnesota's Jane Goodall Institute's Center for Primate Studies. Its director, ecology professor Anne Pusey, is a co-author of the study. The first author is Melissa Emery Thompson of Harvard University. "It is important to distinguish reproductive senescence (aging), which is something animals are expected to experience if they live long enough, from menopause, which is a very unique trait that occurs because reproductive function declines much more rapidly than declines in other bodily systems," said Thompson. "This study of reproductive senescence indicates that chimpanzees do not routinely experience menopause. " According to Thompson, scientists will have to "look to other unique features of human biology and socioecology to help explain why humans have menopause." Human menopause is remarkable in that reproductive deterioration is markedly accelerated relative to the aging of the rest of the body, leaving an extended post-reproductive period for many women, the researchers said. The explanation for that pattern has remained unclear, in part because comparative data from closely related species had been inadequate. Earlier studies of chimpanzees are based on very small samples and have not provided clear conclusions about the fertility of aging females, she said. Also, those studies have not examined whether reproductive declines in chimpanzees exceed the pace of general aging, as in humans, or occur in parallel with declines in overall health, as in many other animals. To remedy those problems, Thompson teamed up with researchers from six long-term chimpanzee research sites across Africa. "By combining our data, we were able to examine the effects of age on fertility rates in chimpanzees," she said. They found that chimpanzee and human birth rates show similar patterns of decline after the age of 40, suggesting that the "biological clock" has been relatively conserved over the course of human evolution. However, in contrast to humans, chimpanzee fertility tends to drop along with their chances of surviving, with healthy females maintaining high birth rates late into life. "When we look at only the healthiest individuals, it looks like chimpanzees may actually be reproducing better than humans in their 40s," Thompson said. "The oldest chimpanzee known to give birth in the wild is estimated to have been 55. She began reproductive cycling again shortly before her death at the age of 63." They thus find no evidence that menopause is a typical characteristic of chimpanzee life histories. "The adaptive significance of human menopause, or post-reproductive lifespan, is still debated," the researchers concluded. "This study provides greater evolutionary context to this debate." Along with recent data from wild gorillas and orangutans, the findings in chimpanzees indicate that "menopause is not a part of the life cycle of living apes and is thus uniquely derived in the human lineage." ---------- |
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